Note that this will not have a visible effect on the results, because the permeability chosen for the open fractures is very high, leading to identical results for the two approaches. However, as mentioned above, the use of interior Neumann-type boundary conditions involves the evaluation of flux continuity conditions at the interfaces between fracture and matrix on the basis of the fracture normal permeability. Here, we are defining scalar permeabilities on the fracture with the result that the normal and tangential permeabilities are the same (if you want them to be different, you have to define tensorial permeabilities). The high value for the "open" fractures leads to neglectable pressure jumps and seems to produce the right results. But, keep in mind that from a physical perspective it makes little sense to define a permeability for an "open" fracture. Using Dirichlet-type interior boundary conditions at the interfaces to "open" fractures is clearly the better choice.
Note that this will not have a visible effect on the results, because the permeability chosen for the open fractures is very high, leading to identical results for the two approaches. However, as mentioned above, the use of interior Neumann-type boundary conditions involves the evaluation of flux continuity conditions at the interfaces between fracture and matrix on the basis of the fracture normal permeability. Here, we are defining scalar permeabilities on the fracture with the result that the normal and tangential permeabilities are the same (if you want them to be different, you have to define tensorial permeabilities). The high value for the "open" fractures leads to negligible pressure jumps and produces results that are visually indistinguishable. But, keep in mind that from a physical perspective it makes little sense to define a permeability for an "open" fracture. Using Dirichlet-type interior boundary conditions at the interfaces to "open" fractures is usually the better choice.
